The Asteraceae

The Aster, Composite or Sunflower Family

Rudbeckia hirta (Asteraceae) black-eyed-Susan	Purple Coneflower (Echinacea purpurea)

The Asteraceae family is one of the largest angiosperm families in the world. It is comprised of 1,160 genera and 19, 085 species. Their distribution is cosmopolitan. In the United States and Canada there are 346 genera and 2, 687 species. The largest genera are Erigeron, Aster, Senecio, Cirsium, Solidago, Eupatorium and Artemisia. The whole family has been divided into two subfamilies, Cichoriodeae (Lactucoideae) and Asteroideae according to their florets and the presence of laticifers. A third subfamily has been proposed, the Barnadesioideae. It has been further divided into at least 17 tribes. The plants are generally herbs or shrubs. The characteristic that ties all of these species together is the flower parts. Each has an inflorescence made up of a capitulum (head) with many tiny florets (flowers) on a receptacle.

Click here for a distribution map of the Asteraceae in the U.S.A.

Vegetative Characters | Reproductive Characters | Diagnostic Characters | Economic Importance/Fun Facts | Evolutionary Adaptations and Relationships | Glossary of Terms | References and Links | Pictures

Vegetative Characters

• anual to perennial herbs, shrubs or trees
• resinous or milky sap
• often have taproots or tubers
• leaves can be simple or pinnately or palmately lobed
• leaves alternate or opposite often in basal rosettes
• leaves can be petiolate or sessile
• inflorescence indeterminate, heads paniculate, racemose, cymose or corymbose in arrangement
• involucre of bracts subtending each head, called phyllaries

Reproductive Characters

• flowers actinopmorphic or zygomorphic
• flowers perfect or imperfect
• flowers epigynous
• monoecious or dioecious
• calyx either absent or a pappus of hairs, bristles, scales or a ring
• corolla sympetallous, 5 lobed, usually tubular(disc floret) or ligulate (ray floret), variety of colors
• 5 epipetalous stamens
• distinct filaments
• connate anthers that form a cylinder around the style
• 1 pistil
• 2 carpels
• inferior ovary with one locule
• basal placentation
• the fruit is an achene, can be compressed, crowned with pappus, winged or spiney
• no endosperm
• large embryo

Diagnostic Characters

• leaves in basal rosettes
• involucre of bracts subtending inflorescence
• small epigynous flowers
• disk or ray flowers
• an inflorescence made up of a capitulum with many tiny florets on a receptacle

Economic Importance/Fun Facts

• food products: sunflower seeds, oil, artichokes, chicory, endive, safflower oil, lettuce
• species from 200 genera used as ornamentals (French marigolds, sunflowers)
• medicinal uses: chamomile, wormwood, colt's foot
• many different weeds including ragweed, dandelions and beggartricks

Evolutionary Adaptations and Relationships

• monophyletic group
• Barnadesioideae is the sister group to the rest of the genera
• Cichorioideae is paraphyletic
• many morphological and molecular synapmorphies

Glossary of Terms

• capitulum- dense inflorescence on a compound receptacle
• taproot- thick main vertical root, direct continuation of radicle, characteristic or gymnosperms and dicots
• tuber- thick, fleshy underground stem
• basal rosette- a circular cluster of the leaves towards the base
• involucre of bracts- whorl of modified, reduced leaves subtending a flower or inflorescence
• phyllary- individual bract if the involucre found in the composites
• pappus- modified out perianth in the composites, consisting of hairs, bristles, scales, awns

References and Links

• Little, John R. and C. Eugen Jones 1980. A Dictionary of Botany. Van Nostrand Reinhold Co. New York.
• Judd et al., 1999. Plant Systematics: a phylogenetic approach. Sinauer Associates, Inc. Sunderland, MA U.S.A.
• Walters, D.R. and D.J. Keil, 1996. Vasccular Plant Taxonomy, Fourth Edition. Kendall/Hunt Publishing Co. Dubuque, IA 52002
• Zomlefer, Wendy B., 1994. Guide to Flowering Plant Families. The University of North Carolina Press Chapel Hill, NC USA.

Pictures

Diagram of disc and ray flowers	Californian thistle Cirsium arvense example of taproot

Helianthus annuusspp.	Cirsium arvense Canadian thistle

Disk Floret	Ray Floret

Marshallia caespitosa	Marshallia caespitosa

opposite leaf orientationSolidago nemoralis	basal rosette of leaces in Musk thistle

For questions or feedback, contact: Catharine Calandra